Microwave phase shifter



Sept. 20, 1 966 (1 NQURSE 3,274,521

MICROWAVE PHASE SHIFTER Filed Sept. 12, 1965 5 Sheets-Sheet l TO SO R EOF PULSE QUREENT FOR SETTING MAGNETIC STATE oF FERRITE. RINGS n "a wInventor Attorneys Sept. 20, 1966 o. NOURSE MICROWAVE PHASE SHIFTER 5Sheets-Sheet 2 Filed Sept. 12, 1963 67/ w/fl x x w n H ay qH Inventor@awa 2W 2 z B 1% j %ttorneys Sept. 20, 1966 Filed Sept. 12, 1963 O.NOURSE MICROWAVE PHASE SHIFTER 5 Sheets-Sheet 5 FIG. 4

M/CAOW/H/E a o a o a MICROWAVE POWH? *1 5%- 1%, F 1727 i 45 i 90 ---P0/4p //v 01/7 APEI/EAFSAL MODULATOR EXECUT/I/E COMMAND A/VD COMMAND wv ur570/25 INPUT 2%? F50 .,,j, SHIFT REG/5TH? M/FORMAT/ON I n um I or M mum.M4444Q44? r W Attorneys United States Patent 3,274,521 MICROWAVE PHASESHIFTER Oswald Nourse, Lee on Solent, England, assignor to NationalResearch Development Corporation, London, England, a corporation ofGreat Britain Filed Sept. 12, 1963, Ser. No. 308,488 Claims priority,application Great Britain, Sept. 19, 1962, 35,651/ 62 Claims. (Cl.333-241) This invention relates to microwave phase shiftersincorporating ferrite material so that the phase shift is controllableelectrically.

Electrically controllable phase shifters have useful properties atmicrowave frequency as they may be used in various configurations toobtain a number of useful devices. Ferrite phase shifters may be classedas reciprocal (in which case the phase shift is the same whichever waythe power is flowing) or non-reciprocal (in which case the phase shiftchanges sign with direction of power flow). Non-reciprocal phaseshifters are particularly considered here as they may be used in theconstruction of circulators. These are devices in which power enters andleaves ports in a certain order, e.g. power enters one arm and leaves bya second arm, enters by the second arm and leaves by a third arm and soon.

In the case of a switchable circulator the order may be reversed ondemand by some external signal which changes, for instance, thedirection of a magnetic field.

With conventional phase shifters used in such switchable circulators itis diflicult to obtain rapid phase shift owing to the system geometrywhich requires that high energy be stored in the magnetic field. Inaddition to this problem the rapidly changing magnetic field causesadverse eddy currents which tend to slow down the change. To overcomethis difficulty, attempts have been made to use closed tubes of ferritematerial but considerable difficulty was experienced in the manufactureof these tubes which were also required to have a rectangular shape ofhigh aspect ratio.

One object of the present invention is to overcome these difiiculties bythe use of commercially available circular ferrite rings and to matchsuch circular rings to the waveguide impedance.

Another object is to ensure that low aspect ratio (circular rings) maybe made to give large phase shift with low loss.

In the present invention, a pulsable phase shifter has circular ferriterings mounted on a dielectric rod with their axes coincident with theaxis of a rectangular waveguide (the dielectric rod on which the ringsare mounted also has its axis coincident with that of the guide), andoptimization of the phase shift is obtained by narrowing the walls ofthe waveguide and matching of the wave into and out of the structure isobtained by suitable adjustment of the spacings between the rings.

Further features of the invention and the constructional details thereofwill be clear from the following description referring to theaccompanying drawings in which FIG. 1 shows a perspective view of oneembodiment of the invention with part of the waveguide structure partlybroken away to show the interior. FIGS. 2 and 3 are a longitudinalsectional view and end elevation respectively of a modified structuregiving progressive variations of phase shift, While FIG. 4 is a blockdiagram of a suitable control system for the structure of FIGS. 2 and 3.For clarity, the conductors are not shown in FIG. 3.

The pulsed microwave phase shifter illustrated in FIG. 1 consists of ahollow rectangular waveguide 1 within which are grouped circular ferriterings 2 threaded on a cylindrical dielectric rod 3, the axes of therings 2 and the rod 3 coinciding with the longitudinal axis of the wave-3,274,521 Patented Sept. 20, 1966 guide. In the region of the groups offerrite rings, the longer transverse internal dimension of the waveguideis reduced or constricted by inwardly projecting portions 4 of thewaveguide walls to increase the amounts of phase shift resulting fromchanges in the magnetic states of the ferrite rings, and thisconstriction of the wider transverse dimension of the waveguide also hasthe incidental advantage of minimizing the number of, and coupling to,unwanted modes of propagation of RR energy along the waveguide.

Pulses of current for altering the magnetization of the ferrite ringsare applied through leads 5 and a metal strip 6 along the middle of therod 3. The dielectric rod 3 is mounted on and supported by theconducting strip 6 which is in turn supported at its ends by the rigidleads 5 passing through insulated sleeves 7 in sockets 8 on the outsideof the waveguide. The ends of the rod 3 can be stepped as shown at 9 forimpedance matching.

In the modified structure illustrated in FIGS. 2 and 3 there is shownanother important aspect of the invention, namely the subdivision ofgroups of the ferrite rings so that more than two different phase shiftsare possible through the device, each subdivision having its own currentlinking path: In this way some groups of the rings can be switchedmagnetically so as to oppose others instead of all the rings beingswitched together into the same magnetic states, which is the case inthe FIG. 1 construction. In the arrangement now to be described, one,two,

.four, eight or sixteen rings may be switched independently by means ofthe thin metal conductors which link these numbers of rings. Thisparticular arrangement can therefore be designated a digital phaseshifter since it accepts a digitally coded input. In FIGS. 2 and 3 isshown an embodiment of a five bit binary coded digital phase shifter forobtaining up to i phase shifts, to an accuracy of i5%, and it isparticularly suitable for the control of the direction of an aerialbeam.

In the digital phase shifter which is illustrated in FIGS. 2 and 3, thestructure is built up from metal and insulated parts held together byscrews 10 and consists of metal end portions 11 of hollow rectangularwaveguide of normal internal dimensions and incorporating end flanges 12for coupling to other structures, and a metal middle portion 13 of thesame internal width as the end portions 11 but constricted in its widercross-sectional internal dimension to nearly one half of thecorresponding dimension of the end portions 11. The metal waveguidewalls have clearance slots 14 through which pass the external leads 5for the conduction of pulsing currents, the leads 5 being secured inplace by strips 15 of rubber or other electrical insulation clampedbetween the metal halves of the waveguide. The cylindrical dielectricrod 3 is supported from the larger end leads 5 and has threaded on itthe circular ferrite rings 2 which are spaced as shown so that groups ofone, two, four, eight or sixteen are linked by individual conductorstrips 6 within the dielectric rod, the ends of said strips beingattached to the external leads 5 as shown. The locations of the endferrite rings on the rod to match into the waveguide impedance and toset the amounts of phase shift achieved by magnetization of the ringsare predetermined by an experimental set-up (not shown) in which RF.power is fed into a waveguide of the same internal dimensions as theconstricted portions illustrated and containing circular ferrite ringsadjustable in position along a dielectric rod, with tapering lossymaterial beyond the adjustable rings to absorb the incoming RF. power,and the positions of the rings are adjusted for a best impedance matchin the usual way with the desired phase shifts, and the ring locationsso determined are used in the final structure.

In the construction shown in FIGS. 2 and 3 a current pulse to the leadand strip through one ferrite ring can produce 15% phase shift, which isa function of its dimensions, in particular the length of the ring alongthe axis of the waveguide, and the axial length of the ring. Thesedimensions can be adjusted experimentally to give the correct phaseshift. A pulse to the lead and strip linking two ferrite rings canproduce i1 At phase shift, or through four, eight or sixteen give phaseshifts of i22 /2, :45", or i90 respectively or in any combinations ofthese amounts.

An example of a control system for a digital phase shifter as justdescribed is illustrated in FIG. 4. An input signal of serially fedphase-angle information from a computer is fed into a shift register andthence to a modulator and store which also receives an executive commandinput and a command reversal input, the five bit output therefrom beingparallel fed control pulses to the phase shifter as in FIGS. 2 and 3 butrepresented by the row of five blocks along the top of FIG. 4 toindicate the different amounts of phase shift obtainable in themicrowave power entering and leaving the phase shifter.

Both the phase shifter constructions described can contain air or inertgas or can be filled with a low-loss liquid dielectric such as liquidparaflin contained between windows across the waveguide at the ends ofthe region occupied by the .ferrite ring assembly.

If greater accuracy than that of a five bit digital phase shifter isrequired it would usually be necessary to further subdivide the deviceand have for instance a seven bit phase shifter. An alternative,however, which may sometimes assist the designer to obtain greateraccuracy, is to use the demagnetized state of each subdivision. Ademagnetized state would prevail in a subdivision immediately after ademagnetizing pulse, after such a pulse this subdivision would have nodifferential phase shift.

A demagnetising pulse would differ from pulses which magnetize the ringsin either one or other of two directions in that after such a pulse thering is demagnetized. Such a pulse could consist of a train of pulses ofalternate sign and gradual decreasing amplitude. This type of pulse isreadily obtainable from well known circuits.

By the ability to apply demagnetizing pulses to any subdivisions itwould be possible to make a digital phase shifter in ternary code. Insuch a device the number of rings in each subdivision would vary in theratio of three to one instead of the previously described two to one.The resultant advantages of the fewer subdivisions would be offset bythe greater complexity in the computing of the correct types of pulserequired for a :given phase shift. The embodiment of such a device wouldbe similar to that shown in FIG. 2 except for the different ratiobetween numbers of rings in the subdivisions.

An alternative to the use of a full ternary coded device would be theuse of a demagnetizing pulse only on the smallest subdivision. In thiscase an extra factor of two in accuracy is obtained without any extrasubdivision of the device, in addition the complication of utilizing theternary code is avoided.

Phase shifters in accordance with the invention have the followingadvantages:

(a) The circular ring geometry has an advantage over others as it is theone that has the lowest flux leakage and hence the energy of switchingis minimized. In addition, as the device is of a field displacementtype, it is of advantage to have the ferrite toroid enclosing themaximum area. The circular geometry achieves this too. Previous deviceshave used 1.7 times the amount of ferrite required by the presentdevice. Hence for a given ferrite the switching energy will be thisfactor lower. For the same reason the losses for a given quality offerrite will be lower.

(b) The use of separate rings of ferrite enables their spacing to be jed to Obtain agood match over a very wide bandwidth. The use of circularrings as opposed to the high aspect ratio rectangular blocks is madefeasible by the narrowing of the spacing between the walls of thewaveguide in the region of the ferrite rings. This has three beneficialeffects: (1) To increase the amount of phase shift for a given amount offerrite material; (2) to flatten the curve of phase shift vs. frequencyso that the device may be used over a wide bandwidth; (3) to minimizethe number of modes in the dielectricferrite-waveguide ensemble, thuslossy resonances may be eliminated over a wide bandwidth.

Another advantage of the use of circular rings is that commerciallyavailable rings of ferrite made for quite a different purpose maysometimes be used, thus reducing the cost of production of the devices.

(c) A digital phase shifter may be more easily constr-ucted usingseparable rings and an arrangement such as FIG. 2 represents a typicalembodiment. The separation of the rings, in any case required forobtaining a match, assists in the routing of the current carryingeonductors required to switch the various groups of rings.

I claim:

1. A mircowave phase shifter for pulsed operation comprising a hollowwaveguide of rectangular crosssection having within it a cylindricaldielectric rod disposed with its longitudinal axis coincident wth thelongitudinal axis of the waveguide, an assemblage of circular rings offerrite threaded on said rod and mounted thereon in predeterminedlocations along it, a metal strip along saidrod and external leadsconnected to the strip for the conduction of pulsing current throughsaid strip, and constriction of the wider internal cross dimension ofthe waveguide, which constriction extends along the region occupied bythe ferrite ring assemblage to enhance the effective phase shiftresulting from magnetization of the ferrite rings by the pulsingcurrent.

2. A microwave phase shifter as claimed in claim 1 wherein the ferritering assemblage comprises individual groups of rings with a separatepulse conducting strip linking each group.

3. A microwave phase shifter as claimed in claim 1 and having theferrite ring assemablage formed by separated sets of rings arranged as abinary power sequence of numbers of rings per set with a separate pulseconducting strip linking each set.

4. A microwave phase shifter as claimed in claim 1 and filled with aliquid dielectric contained between windows across the guide at the endsof the region occupied by the ferrite ring assembly.

5. A microwave phase shifter as claimed in claim 1 and built up frommetal end portions of hollow rectangular Waveguide in two longitudinalhalves and having end flanges for coupling to other structures and ametal middle portion, also in two halves, of waveguide constricted inits wider cross-sectional internal dimension, said portions beingsecured together and having clearance slots around the pulse conductionleads which are held in place and insulated from the metal parts byrubber strips clamped between the half portions of waveguide.

OTHER REFERENCES Lax et al.: Microwave Ferrites and Ferrimagnetics,

McGraw-Hill, New York, N.Y., 1962, p. 569.

Proceedings of the IRE, vol. 44, No. 10, October 1956, p. 1420.

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GLENSLER, Assistant Examiner.

1. A MIRCOWAVE PHASE SHIFTER FOR PULSED OPERATION COMPRISING A HOLLOWWAVEGUIDE OF RECTANGULAR CROSSSECTION HAVING WITHIN IT A CYLINDRICALDIELECTRIC ROD DISPOSED WITH ITS LONGITUDINAL AXIS COINCIDENT WITH THELONGITUDINAL AXIS OF THE WAVEGUIDE, AN ASSEMBLAGE OF CIRCULAR RINGS OFFERRITE THREADED ON SAID ROD AND MOUNTED THEREON IN PREDETERMINEDLOCATIONS ALONG IT, A METAL STRIP ALONG SAID ROD AND EXTERNAL LEADSCONNECTED TO THE STRIP FOR THE CONDUCTION OF PULSING CURRENT THROUTHSAID STRIP, AND CONSTRICTION OF THE WIDER INTERNAL CROSS DIMENSION OFTHE WAVEGUIDE, WHICH CONSTRICTION EXTENDS ALONG THE REGION OCCUPIED BYTHE FERRITE RING ASSEMBLAGE TO ENHANCE THE EFFECTIVE PHASE SHIFTRESULTING FROM MAGNETIZATION OF THE FERRITE RINGS BY THE PULSINGCURRENT.